Securing Gmail (old phonenumber)

Seller: kuraika

So i sucessfully bought a game account with mm. The game does not allow to change email so now i have one small problem. So this question somewhat implies that i dont 100% trust the MM that handled my transaction not because i dont like him but i dont trust anyone on the internet 100% I did changed pretty much everything possible on the gmail even the phone number backup email etc. But the old backup phone now still lingers on the email for i think 14 days or something. Considering i changed everything possible and logout out every device could the gmail be stolen back just with that old phone number ? Can i even do anything against this?. Anything i want to change or do requires the old phone number. Asking because i really assumed that i could 100% secure the account, but was show otherwise. Just to make it clear i had a wonderfull experience with the MM and would wish for nothing more that that would stay that way so no one has to get offended